Goals: This was the fifth and last (following Pioneers 6, 7, 8, and 9) of a series of solar orbiters intended to study, from widely separated points in space on a continuing basis, interplanetary phenomena such as the Sun's magnetic field, the solar wind, and solar and galactic cosmic rays.

Accomplishments: None. Failure of the booster's first stage caused the launch vehicle to veer off course. Ground control destroyed the rocket about seven minutes into the flight, before Earth orbit could be achieved.